Detector system for television receivers



,Aug.' 11, 1942. l.. 'RQ MALLING DETECTOR SYSTEM FOR TELEVISION RBSJEIVERS I Filed Apxfil 18. 1940,-

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UNITED STATE s PATENT ori-ICE- DETECTOR SYSTEM Fon TELEvIsIoN nEcErvEnS.

Leonard B.. Mailing, Douglaston, N. Y., assigner to Hazeltine Corporation, a corporation of Del- Applicationy April` 1s, 1940, serial No. 330,211

s claims. (ci. 11s-'1.3)

the signal input to the reproducingl device the as possible, both for the reason that the cost or the receiver is thereby reduced and for the reason that the over-all distortion in thesignaltranslating channel is likely lto be less. Also, if a Isignal is raised to a high amplitude level in the intermediate-frequency channel of a television receiver, some useful limiting can be eiected in a systemwhere the synchronizing-signal components have a greater amplitude than the videofrequenciy components 'for the reason that noise or other spurious components of greater amplitude than that 'of the desired signal components can be substantially limited without 'adversely aiiecting the signal reproduction. However, the detection of the modulation components of the signalmust also be effected-with a minimum of distortion. It is, however,` apparent that, if highlevel detection can be eiected without an undue amount of distortion, there is no need to provide astse of video-frequency ampliiication in the receiver. stage or stages can be avoided, there is no need synchronizing-signal components thereof generally must be of negative polarity. It is desirable,

therefore, to provide a high-level detector from which signals of opposite polarity may be applied directly to the signal-reproducing device of the system and to the synchronizing channel oi the system, respectively.

It is an object ofthe present invention, therefore, to provide an improved'high-level detector system for a television receiver.

It is another object of the invention to provide a high-level detector system for a television receiver which is eiective to ysupply output signals of opposite polarities directly to the signal-reproducing, device and to the synchronizing-sign channel, respectively, of the receiver.

In accordance with the invention, there is provided in a television receiver including an imageput circuits. Means are provided for applying Furthermore, if the video-frequency` for the usual additional arrangements which are provided for reinserting the unidirectional-background components oi the signal at the input of each stage of the video-frequency channel of the television receiver. Y Q

Other diillculties, however, arise in a high-level lsignal detector system. For instance, synchrobut they must be obtained therefrom with the.

proper polarity. In the usual synchronizing-signal separator for television receivers, separation of the synchronizing-signal components from the vision-signal components is eiected by operating a vacuum tube beyond its negative grid-voltage cutoilpoint for video-signalcomponents. Such operation' requires that the signal input to the separating device be of such polarity that the synchronizing-signal peaks are positive, whilein 4:so

reproducing device anda synchronizing-signal separator, and adapted toreceive a carrierl signal modulated by video-frequency components and. synchronizing-signal components of greater amplitude than the video-frequency components, a detector system comprising a high-level anodecircut, single detector tube havinginput and outthe received signal to the input circuit of the detector with such amplitude that components ,of greater amplitude than that of the synchronizing-signal components are substantially limited in the detector. Means are further provided for rectifying in the input circuit oi the detector at coupling the output'circuit o'f the detector to the image-reproducing device of -the receiver to supply thereto the detected modulation signal with `a given polarity. Means are further provided for deriving from the output circuit of the detector the 'modulation signal having a polarity opposite to that oi! theA iirst-named derived modulation signal and adapted Vfor application toy the synchronizing-signal separating apparatus.

thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a circuit diagram, partly schematic, of a complete television signalreceiving system including a detector system in accordance with the invention; Figs. 2a and 2b comprise a number of graphs utilized to explain the operation of the detector system of the receiver of Fig. 1; while Fig. 3 is a circuit diagram of a modiilcation of the detector system -illustratedin the receiver of Fig. 1.

Referring now more particularly to Fig. 1, the receiver there illustrated is adapted to receive a carrier signal modulated by video-frequency components and synchronizing-signal components of greater amplitude than the video-frequency components and comprises the vision signal-translating channel of a television receiver of the superheterodyne typeincluding an antenna system I0, I I connected to a radio-frequency amplifier I2 to which are connected in cascade, in the order named, an oscillator-modulator I3, an intermediate-frequency amplifier Il, a detector and A. V. C. supply indicated generally at l5 embodying the present invention and described in detail hereinafter, and an image-reproducing device I6 usually of the cathode-ray tube type. A line-scanning generator I1 and a field-scanning generator I8 are also coupled to an output circuit of detector I5 through an intersynchronizing-signal separator I9 and to the scanning elements of the image-reproducing device I6. 'I'he stages or units III-I9, inclusive, excepting the detector system I 5, may all be of conventional wellknown construction so that detailed illustrations and descriptions thereof are unnecessary herein.

Referring briefly to the operation of the receiving system Just described, television signals intercepted by the antenna circuit III, II are selectively ampliiied in radio-frequency amplier I2 and supplied to the oscillator-modulator I3 wherein they are converted to intermediate-frequency signals which, in turn, are selectively amplified in the intermediate-frequency amplifier I4 and delivered to the detector I5. The modulation components of the signal are derived by the detectori 5 and supplied directly to the brilliancycontrol electrode-of the image-reproducing device I6 with proper polarity for signal reproduction. The intensity of the scanning beam of device I 6 is thus modulated or controlled in accordance with the video-frequency voltages impressed upon its brilliancy-control element in the usual manner. The modulation signal is also applied with opposite polarity directly to synchronizingsignal separator I9, wherein the synchronizing signals are separated from the video-frequency components of the received signal and from which the synchronizing signals are applied to generators I1 and I8 to synchronize the operations of these generators with corresponding apparatus at the transmitter. Saw-tooth current or voltage scanning waves are generated by the generators I1 and I8 and these waves are applied to the scanning elements of the device I6 to produce scanning ilelds, thereby to deilect the scanning beam in two. directions normal to each other so as to trace successive series of parallel lines or --flelds on the target of the image-reproducing device to reconstruct the image. A

Referring now more particularly to the portion amazes ot the system of Fig. 1 embodying the present invention,` detector I5 comprises a high-signallevel detector system including a single pentode detector tube 2l having input and output circuits to the input 'circuit of which the received signal is applied from theoutput circuit oi.' intermediatefrequency amplier Il with such amplitude that components of greater amplitude than the synchronizing components are substantially limited in the detector. The input circuit of tube 2l comprises a coupling condenser 2i and a gridleak circuit including resistors 22 and 23 in series. A trap circuit 24, 2l may be included in the cathode circuit of tube 2l in order to provide increased attenuation of undesired signals on adjacent channels. A direct current passive network is provided for coupling the anode ot vacuum tube 2l to the input circuit ot image-reproducing device I6 to supply thereto detected video-frequency components o! the signal with a given polarity. This network includes a load resistor 21 in series with a parallel-resonant circuit 2l, 2l through which a unidirectional operating potential is supplied to the vacuum tube 2li.' 'I'he network also includes shunt arms comprising condensers 3l, 3i and an interposed series arm including a parallel-resonantycircuit 32, 33.

In order to derive from the output circuit of tube 2l detected synchronizing-signal components of the received signal having a polarity opposite to those supplied to the image-reproducing device I6, there is provided a cathode load circuit which includes a resistor 35 by-passed for intermediate-carrier-frequency currents by condenser 36. The voltage across resistor 35 is applied through a illter comprlsinga series-inductance arm 31 and a shunt-capacitance arm Il to ttie lirsiput circuit of synchronizing-signal separa- Reference is made to tlie graphs of Figs. 2a and 2b for an explanation of the operation of the detector system I5 of the receiver of Fig. 1. In Fig. 2a, the curve A represents the grid voltage-anode current characteristic of tube 20. while curve B represents the grid-voltage-grid current characteristic of tube 20. The modulation envelope of the signal applied to the input circuit of de- 1 tector I5 is also represented and comprises synchronizing-slgnal components S and video-frequency components V. Under normal operating conditions at least a portion ofthe synchronizingsignal components are rectiiled in the input circuit of the tube 20 and the condenser 2| and the resistors 22, 2l are effective so to bias the input electrode of vacuum tube 20 that grid current is obtained only from the peaks of the synchronizing-signal components of the applied modulation signal, as illustrated by the relationship of the modulation envelope of Fig. 2a to the grid voltage-grid current characteristic B of tube 2l. There is, therefore, developed across resistors 22, 23 a voltage which varies in accordance with the peak amplitude of the received signal, independent of its modulation components, which voltage is used to provide an operating bias for the detector 20 to eiect anode-circuit detection therein. Since the voltage across resistors 22, 2l varies in accordance with the amplitude of received signals, independent of light-modulation components thereof it is also suitable for use as an automatic amplification control bias for the receiver and, for this reason, the mid-point of resistors 22, 23 is connected by the conductor labelled A. V. C. to one or more of the tubes of stages I2, Il, and I4, thereby providing automatic ampliiication control in a manner which will be understood by those skilled in the art.

The anode current-anode voltage characteristics of the tube 2l for various bias voltages are illustrated in Fig. 2b. 'Ihe'load circuit oi the detector tube 2l is so proportioned that it operates upon a load line as indicated by the dotted line L in a manner which will be well understood by those skilled in the art, the output voltage of the detector being represented by the wave form 0. 'I'here is thus developed across resistor 21 in the anode circuit of tube 2l a voltage having the same wave form as curve O of Fig. 2b in which synchronizing-signal components are negative with respect to the video-frequency components thereof, as indicated by the curve adjacent resistor 21 of Fig. 1. There is also developed across resistor 3i in the cathode circuit of tube 2l a voltage of the same wave form, but of opposite polarity, as indicated by the wave form adjacent resistor 35 of Fig. 1. this latter voltage being applied to synchronizing-signal separator il and being of the proper polarity to operate the first vacuum tube thereof beyond its negative grid-voltage cutofi point for' video-frequency components of the detected signal.

The detector system oi Fig'. l is. therefore, such that high-level anode-circuit detection is 'effected by the vacuum tube and the signal input thereto may be of such amplitude that components of amplitude greater than the synchronizing-signal components are substantially limited in the detector. Since a high-level detected signal output is derived from the tube 20video-frequency amplification may be dispensed with and the direct current passive network can beutilized for coupling the output circuit of the detector 20directly to the image-reproducing device i6 of the receiver. With such an arrangement, there is no need for devices for inserting the unidirectional background illumination component voi the received signal for the reason that these components are present in the output circuit of tube 2l and are transmitted by the direct current network 30, 3l, 32, 33.

In Fig. 3 there is illustrated a detector system in accordance with the invention which is generally similar to that of the detector system i5 of Fig. 1. Circuit elements which are identical in the two iigures have the same reference characters. It will be understood that the detector system of Fig. 3 can be utilized in the receiver circuit of Fig. l by connecting terminals A, B, C, and D to the similarly marked terminals rof the receiver of Fig. 1. No provision is made in the detector system of Fig. 3 for providing an automatic amplication control for the receiver.

The circuit of Fig. 3 differs from that of Fig. 1

to any particular circuit elements, there follows a list of circuit constants whichhave been found to be particularly suitable for the circuit of Fig. 3,

where the intermediate-frequency signal hara.

carrier frequency of 8.5 megacycles:

primarily in the fact that in the circuit o1 Fig. 3

there is no rectification inthe input circuit of va'cuum tube 20 to provide an operating bias for the tube. Instead, there isprovided in the cathode circuit of tube 20 of Fig. 3, a resistor 40, by-passed for intermediate-frequency and modulation-frequency signals by `a condenser I i across which is developed a unidirectional voltage eilective to bias the input circuit of vacuum tube 2l for anode-circuit detection.

The operation of the system of Fig. 3 is generally s imilarlto thatdescribed for'the circuit of Fig. 1 and, with the above explanations of the differences between the circuits of Figs. 1 and' 3, will be readily understood by those skilled in the art.

While it is not .intended to limit the invention While Ithere have been described what are at present considered to be the preferred .embodiments of this invention, it will be obvious to tho skilled in the art that various changes and modications, may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spiritv and scope of the invention.

Wh'at is claimed is: 1. In a television receiver including an image- I reproducing device and synchronizing-signal separatng apparatus and adapted'to receive a carrier signal modulated by video-frequency components and synchronizing-signal components of greater amplitude than said video-frequency components, a detector system comprising, a high-level anode-circuit single detector tube having input and output circuits, means for applying the received signal to said input circuit with such amplitude that components of greater amplitude than said synchronizing-signal components are substantially limited in said detector, means for rectifying in said input circuit at least a portion of said synchronizing-signal components to provide an operating bias for said detector, means for deriving an automatic ampliiication control bias for said receiver from said input circuit, a direct current passive network for coupling said detector output circuit to the image-reproducing device of the receiver to supply thereto the detected modulation signal with a given polarity,

and means for deriving from said output circuit the detected modulation signal having a polarity opposite to that of said first-named derived modulation signal and adapted for application to said synchronizing-signal separating apparatus.

2. In a television receiver including an imagereproducing devicev and adapted to receive a carrier signal modulated by video-frequency components and synchronizing-signal components of greater amplitude. than said video-frequency components, aA detector system comprising, a high-level anode-circuit single detector tube hav- .ing input and. output circuits, means included in one of said circuits for substantially limiting in said detector components of the received Signal oi greater amplitude than said synchronizingsignal components, and a direct current passive network coupled to said detector output circuit and adapted to couple said detector output circuit directly to said image-reproducing device of the receiver to supply thereto detected video-frequency components of said signal including the direct current component thereof.

3. In a television receiver including an imagereproducing device and synchronizing-signal separating apparatus and adapted to receive a carrier signal modulated by video-frequency components and synchronizing-signal components of greater amplitude than said video-frequency components. a detector system comprising, a high-level anode-circuit single detector tube having input and output circuits, means for applying the received signal to said input circuit, a direct current passive network coupled to said detector output circuit and adapted to couple said detector output circuit to the image-reproducing device of the receiver to supply thereto the detected modulation signal with a given polarity, and means for deriving from said output circuit the detected modulation signal having a polarity opposite to that of said first-named derived modulation signal and adapted for application to said synchronizing-signal separating apparatus.V

4. In a television receiver including an imagereproducng device and synchronizing-signal separating apparatus and adapted to receive a carrier signal modulated by video-frequency components and synchronizing-signal components of greater amplitude than said video-frequency components, a detector system comprising, a high-level anode-circuit single detector tube having a cathode and input and output circuits,l

means for applying the received signal to said input circuit, a direct current passive network included in circuit with said anode and adapted .to apply to the image-reproducingdevice of the receiver the detected modulation signal with a given polarity, and a load circuit connected in series with said cathode for deriving -the detected modulation signal with a polarity opposite to that of said iirst-named derived modulation signal and adapted for application to said synchronizingsignal separating apparatus. 5. In a television receiver including an imagereproducing device and synchronizing-signal separating apparatus and adapted to receive a carrier signal modulated by video-frequency components and synchronizing-signal components of greater amplitude than said video-frequency components, a detector. system comprising, a high-level anode-circuit single detector tube having input and output circuits, means for applying the received signal to said input circuit, means for rectifying in said input circuit at least a portion of said synchronizing-signal components to provide an operating bias for said detector, means for deriving an automatic amplification control bias tor said receiver from said in-V put circuit, a direct current passive network coupled to said detector output circuit and adapted to couple said detector output circuit to the image-reproducing device of the receiver to supply thereto the detected modulation signal with a given polarity, and means for deriving from said output circuit the detected modulation signal having a polarity opposite to that of said iirstnamed derived modulation signal and adapted for application to said synchronizing-signal separating apparatus.

6. In a television receiver including an imagereproducing device and synchronizing-signal separating'apparatus and adapted to receive a carrier signal modulated by video-frequency components and synchronizing-signal components of greater amplitude than said video-frequency components, a detector system comprising, a high-level anode-circuit single detector tube having input and output circuits, means for apply-v ing thereceived signal to. said input circuit with such amplitude that components of greater amplitude than said synchronizing-signal components are substantially limited in said detector, a direct current passive network coupled to said detector output circuit and adapted to couple said detector output circuit to the image-reproducing device of the receiver to supply thereto the de- -tected modulation signal with' a given polarity, and means for deriving from said output circuit the detected modulation signal having a polarity opposite to that of said first-named derived modulation signal and adapted for application to said synchroniz'ng-signal separating apparatus.

LEONARD MALLING. 

